Fluid TherapyElectrolytesIsotonic SolutionsColloidsWater-Electrolyte BalanceRehydration SolutionsHyponatremiaPlasma SubstitutesHypovolemiaIntraoperative CarePerioperative CareColorectal SurgeryBlood Volume DeterminationGoalsHydroxyethyl Starch DerivativesSodium ChlorideWater-Electrolyte ImbalancePostoperative CarePostoperative ComplicationsHemodynamicsSodiumProspective StudiesPotassiumTreatment OutcomeChloridesHypernatremiaHypokalemia